The present invention relates to a medical instrument, with a cannula through which shafts of other instruments having different shaft diameters can be guided, with a seal comprising an opening with a variable opening cross section through which the shafts having different shaft diameters can be guided sealingly, with an expansion device for expanding the opening of the seal, which expansion device has an expansion cone with a plurality of slats that are mounted pivotably on an annular body and form an expansion body that narrows from the proximal end to the distal end and that is connected at the distal end to the seal in the area of the opening.
A medical instrument of this kind is known from EP 0 696 459 B1.
Said medical instrument is a trocar that is used in minimally invasive surgery. The trocar is introduced through a small opening, which is formed by a small incision in the skin for example, through the abdominal wall into the abdominal cavity of the patient by means of a trocar mandrel. After removal of the trocar mandrel, shafts of other instruments used for the surgical intervention are then passed through this trocar. These instruments include, for example, gripping tools, coagulation instruments, endoscopes and the like. These have shafts of different diameters.
Since minimally invasive interventions of this kind are often performed during insufflation of the internal cavity in which the operation takes place, all the intervention points must be gas-tight.
In the aforementioned EP 0 696 459 B1, this purpose is served by an elastic conical seal that is arranged in the trocar and that narrows from the proximal end to the distal end. To permit a uniform widening of the seal when an instrument of a diameter larger than the opening in the seal is inserted into the trocar, an expansion cone is arranged in the proximal direction from this seal. An instrument inserted into the expansion cone expands the latter radially, which in turn widens the opening in the seal. The expansion cone also prevents damage to the seal during insertion of sharp-edged instruments.
Upon insertion of an instrument having a shaft diameter corresponding approximately to that of the cannula of the trocar, the instrument expands the opening to the maximum extent, and the whole circumference of the shaft comes uniformly into contact with the seal. In this way, the trocar system is sealed off at the proximal end. Whenever a shaft of an instrument is inserted into the opening of the seal, said shafts having a diameter of at least the opening or larger.
Insertion of an instrument having a slender shaft which is only a little bit larger than the original size of the opening can become offset from the central passage through the opening of the seal. Moreover, particularly in the case of narrower flexible shafts, the shaft may tilt in the trocar.
Both of these situations have the effect that the seal does not come uniformly into contact with the shaft about the whole circumference of the latter. This results in undesirable leaks. These lead to an escape of the gas, which has been admitted for the operation, and, consequently, to a loss of the insufflation.
The insertion of instruments with narrow shafts can therefore be problematic and may cause difficulties.
It is therefore an object of the present invention to develop a medical instrument of this kind in such a way that a lateral offset of an inserted shaft cannot lead to a loss of leaktightness of the trocar.